The mantis shrimp, a marine crustacean, is widely recognized for its extraordinarily powerful, lightning-fast strike. Far more complex is the creature’s visual system, which many scientists consider the most elaborate in the animal kingdom. These animals possess a pair of stalked eyes that move independently, granting them a unique perspective on their underwater environment. The exceptional nature of their vision has led to a persistent myth suggesting they can see light beyond the human visual range, including thermal infrared radiation. However, the true complexity of their eyesight lies not in detecting heat but in processing a vast spectrum of colors and light properties invisible to us.
Beyond the Infrared Myth: Their True Spectral Range
The notion that mantis shrimp can see true thermal infrared light—the long-wavelength radiation associated with heat—is inaccurate. Their visual range does not extend into that deep-red, low-energy part of the spectrum. Instead, their spectral acuity is concentrated at the high-energy end of the light spectrum, extending well into the ultraviolet (UV) range. Their visible spectrum spans from roughly 300 nanometers (deep UV) up to 720 nanometers, including far-red light.
The core of their hyperspectral ability is housed in a retina containing at least 12 different types of photoreceptor cells, a dramatic increase compared to the three types found in human eyes. This high channel count allows them to perceive an extensive array of colors, extending vision into the UV range where many communication signals occur. Despite this, mantis shrimp are surprisingly poor at discriminating between very similar colors compared to humans. Scientists hypothesize their system functions less like fine-tuned color comparison and more like a rapid, parallel processing system for color recognition, enabling quick identification of specific spectral bands without needing high-resolution color distinction.
The Complex Anatomy of Mantis Shrimp Eyes
The mantis shrimp eye is a compound eye composed of thousands of individual light-sensing units called ommatidia. Each eye is divided into three distinct sections: the dorsal hemisphere, the ventral hemisphere, and a unique, six-row structure known as the mid-band. This three-part division gives the mantis shrimp a rare capacity for monocular range-finding, allowing a single eye to perceive depth by focusing on an object with three different regions simultaneously.
The mid-band is the most specialized part of the eye, containing photoreceptors responsible for extensive color and polarization detection. The first four rows house spectral photoreceptors sensitive to wavelengths from UV to far-red. The remaining two rows are dedicated to detecting different forms of polarized light. The specialized ommatidia in this mid-band act as an optical scanner that the mantis shrimp sweeps across a scene to gather visual data.
The Power of Polarized Light Detection
The mantis shrimp’s most famous visual capability is the detection of polarized light, a property generally invisible to humans. Polarized light is light in which all waves vibrate along a single plane, created naturally by reflections off water or biological surfaces. Mantis shrimp are sensitive to linear polarization and are one of the few animal groups known to detect circular polarization.
Circularly polarized light is a unique form where the light wave spirals in a helix, either clockwise (right-handed) or counter-clockwise (left-handed). The mechanism for detecting this property is housed within the photoreceptors located in the fifth and sixth rows of the mid-band. A specialized structure, the rhabdomere of the distal R8 photoreceptor cell, functions as a quarter-wave retarder. This biological filter converts incoming circularly polarized light into linearly polarized light. The resulting linear light is then detected by underlying photoreceptor cells, allowing the animal to distinguish between the two different directions of the spiraling light.
How Advanced Vision Shapes Mantis Shrimp Behavior
The mantis shrimp’s advanced visual system is intricately linked to its survival and complex social life on the coral reef. The ability to see both linear and circular polarized light provides a means of secret communication, as these signals are often invisible to most predators and competitors. Mantis shrimp use polarized patterns on their bodies during territorial and mating displays to signal intent and species identity.
Circular polarization may be used for highly specialized communication, such as assessing the occupancy of a burrow before a dangerous encounter. Their UV vision is utilized for communication and enhancing contrast, which assists in finding camouflaged prey or spotting predators. This system allows for rapid color recognition and target acquisition, an advantage for an animal that relies on a single, devastating strike to secure a meal. The combination of hyperspectral and polarization sensitivity gives the mantis shrimp an unparalleled ability to navigate their visually complex underwater world.